The present invention relates to a process for preparing alpha-hydroxycarboxylic acids by a reductive double carbonylation of organic halides.
Alpha-hydroxycarboxylic acids, such as lactic acid, alpha-hydroxybutyric acid and alpha-hydroxyoctanoic acid, are important industrial products. They are used either directly (for example in the foodstuffs field, in the case of lactic acid), or as intermediates in organic synthesis.
There are various access routes to alpha-hydroxy acids. The most advantageous from the industrial standpoint are (1) fermentation (preparation of lactic and alpha-hydroxybutyric acids, in particular), (2) hydrolysis of alpha-halocarboxylic acids in alkaline medium and (3) acid hydrolysis of aldehyde cyanohydrins (alpha-hydroxynitriles).
Regardless of the value of these various processes, they are limited by certain disadvantages. Thus, fermentation processes are not of general use, and lead to complex mixtures from which the recovery of the alpha-hydroxy acid sought proves complicated. The organic synthesis processes involve the preparation of starting substances by carrying out multi-stage methods (preparation of alpha-halo acids or alpha-hydroxynitriles, for example).
For all these reasons, the industry continues to seek processes for preparing alpha-hydroxy acids employing readily accessible reagents. The present invention relates to such a process.
More specifically, the present invention is a process for preparing alpha-hydroxycarboxylic acids, comprising the step of reacting an organic halide with carbon monoxide and a hydrogen donor compound, in the presence of a carbonylation catalyst and an inorganic base, at a temperature of at least 90.degree. C.